Increasing and more difficult challenges are being placed on electrical test probing, especially wafer probing. Advances in semiconductor technology, such as increased I/O count, tighter geometries, and higher numbers of dies per wafer are leading to a need for improvements in test probe methods and apparatuses. Improvements are needed in, among other places, probe tip reliability and usage.
Probe cards are used to test electronic devices at the wafer level. Repeated use typically results in a buildup of debris collected from the wafer surface, generally including hardmask material, which can result in poor or no electrical contact, resulting in an incorrect identification of the device under test as a failing device. Thus, probes on the cards need to be cleaned regularly, and if this is not done, then electrical measurements can be greatly affected.
Current art has the probes, after a specified number of test operations (or “touchdowns”), placed against a rough or abrasive pad and “scrubbed” to clean the tips. This scrubbing transfers the debris from the probe tip to the cleaning material. In order for the tips to be properly cleaned, the next time a scrubbing operation is required, the probes are placed in a “clean” spot on the pad to prevent picking up debris from a previous scrub. This general process continues until the wafer prober has completed scrubbing on the entire available pad area, at which point the prober is “reindexed” to the first location on the pad, and continues to reuse the pad until it is changed.
While it is possible for the prober to indicate that a new cleaning pad is required, even if it is indicated, there is no requirement that the pad actually be changed. Moreover, changing the cleaning pad is a time and labor intensive effort, during which the wafer prober is not operative, and products are not being tested.
Also, it is known that scrubbing alone might not be sufficient, because after scrubbing, debris might still cling to the probe tips. A prober may, therefore, be equipped with a brush that the probes are inserted into and removed, thereby removing debris from the probes. However, debris remains in the brush, and can actually be transferred back onto the probes the next time they are inserted. Thus, the brush needs to be periodically removed and cleaned or replaced.
In addition to cleaning pads with abrasive material, cleaning pads with adhesive films or gels are also known. When such materials are used, the probe tips are generally “dipped” into the cleaning pad, rather than scrubbed across the surface, and loose contaminant particles are intended to be retained in the adhesive or gel. Such adhesive and/or gel materials can transfer to the probes, and, in turn, to the wafers, both of which are undesirable.